1. Field of the Invention
The present invention pertains to guide devices for hand-held electric drills.
2. Description of the Prior Art
The patent literature shows a wide variety of devices for guiding hand-held electric drills. One common type of guide device acts by constraining the drill bit itself. Guides of this type are disclosed in U.S. Pat. Nos. 2,788,684 to Scharf, 3,381,551 to Lavering et al., 3,661,469 to Leff et al., and 4,253,784 to Anderson. Many of the guides of this type employ bushings to hold the bit. Such guides can only be used with drill bits that fit the bushings provided. Another drawback is that extra-long bits are often called for, since they must be long enough to pass through the bushing and still drill a sufficiently deep hole.
Another common type of drill guide is that in which the drill is affixed to a moveable stage or rod whose motions are guided. Examples of this type of guide are U.S. Pat. Nos. 2,997,900 to Pugsley, 3,838,935 to Boyajian, 3,853,420 to Abell, 3,890,058 to Self et al., 3,874,810 to Russell, 4,082,474 to Stiger, 4,314,782 to Beekencamp and 4,375,341 to Schulze. Many of the guides in this category offer a variety of features. However, affixing the drill to the stage can be a difficult and time consuming process.
Two popularly used guides from this group are U.S. Pat. Nos. 3,874,810 to Russell and 4,375,341 to Schulze. These devices offer a number of useful features and also have simple designs which can be manufactured economically. To use either of these devices, the chuck is removed from the drill and screwed onto one end of the device, while the body of the drill is screwed onto the other. However, chuck removal can be a difficult process. To loosen a standard drill chuck, the chuck key is inserted and banged sharply with a mallet or piece of wood. The user must be aware that the chuck has a reverse thread. With reversing drills, it is also necessary to remove a reverse-threaded screw inside the chuck. Also, not infrequently, chucks become jammed and refuse to loosen. Once the guided holes have been made it may then be necessary to remove the drill from the guide and reassemble it. Consequently, the use of these guides may not be worthwhile when only a small number of guided holes are to be drilled.
U.S. Pat. No. 3,107,556 to Pugsley discloses a guide which has a number of useful features and does not require that the drill be affixed to a moving stage. With this device, a specially designed cylindrical drill is set up simply by inserting it into a tubular guide. The drill is then guided by a sliding action. However, this design has limitations also.
Unlike an ordinary drill, where the grip projects from the side, the Pugsley drill has a "saw-type" handle attached to the end, where it will not interfere with the guide tube. The cylindrical drill housing also appears bulkier than that of an ordinary drill, to the extent that a user probably could not wrap his or her hand around it. These factors would make the drill difficult to handle when drilling holes without the guide.
The guide of Pugsley is apparently constructed of an opaque material, providing "a window (opening) through which the tip of the drill bit may be visually observed". This type of construction would interfere with the illumination of the work piece and would only permit viewing from a certain angle. This arrangement also fails to provide eye protection, since there is no protective transparent material directly between the viewer's eye and the drill bit.
The Pugsley guide includes two retractable legs which may be extended to tilt the guide for drilling angled holes. While this is a useful feature, it would be preferable if only a single member required adjustment for drilling angles. The patent also notes that longer bits may be required for drilling angled holes.
Another limitation is that, to compensate for wear, shimming may be required "to insure a relatively close fit of the drill and guiding member".
Still another limitation of Pugsley is its size and complexity, which would tend to increase its manufacturing cost relative to other drill guides.
The above limitations are overcome in the present invention.